OBJECTIVES: 1. We are evaluating the relationship between unbound bilirubin concentration and various aspects of bilirubin toxicity in tissue culture and mitochondria. These include ion leakage, oxidative metabolis, glycolysis, and ATP levels. Particular attention is given to the sequence of events as cells are exposed to higher concentrations of bilirubin. 2. In an effort to understand the reasons for altered serum binding in sick infants we will study the relationship between plasma free fatty acid levels and serum binding of bilirubin using GLC and the peroxidase method. 3. We are evaluating the mechanism of enzymatic oxidation of bilirubin and are attempting to identify products of the reaction.